1. Field of the invention
This invention relates to a hermetically sealable package for electronic component. More particularly, the invention relates to a hermetically sealable package for appropriately sealing a functional device such as an electronic circuit for high frequency region provided on an alumina substrate in the form of a thick or thin layer hybrid integrated circuit, an elastic surface wave element provided in layers on a high dielectric material for high frequency, or a filter.
2. Description of prior arts
Certain electronic components such as an electronic circuit for high frequency region provided on an alumina substrate in the form of a thick or thin layer hybrid integrated circuit, an elastic surface wave element provided in layers on a high dielectric material for high frequency, a filter, and other functional devices are generally encased in a hermetically sealed package for the purpose of maintaining their functions stably for a long period.
For instance, a package illustrated in FIG. 1a in the attached drawings is employed. In FIG. 1a, the package is composed of a base member 11 and a lid member 12. The base member 11 comprises a bottom plate 13 and a side wall 14 which extends upwardly from the periphery of the bottom plate 13. The bottom plate 13 and side wall 14 are generally made of metal such as iron or an alloy. The side wall 14 is provided with insulating portions 15, through which lead wires 16 penetrate. The insulating portion 15 is generally made of glass. The top of the wall 14 is to be welded with the periphery of the lid member 12 to seal the package. On the top of the wall 14 is formed a protrusion 17 for facilitating the welding. The welding is generally performed through resistance welding. FIG. 1b is a vertical section of the base member of the package illustrated in FIG. 1a, which is taken along the line I--I. As shown in FIG. 1b as well as in FIG. 1c which is an enlarged view of the portion A of FIG. 1b, the protrusion 17 has a pointed top.
As described above, the protrusion is formed on the base member for facilitating the welding between the base member and the lid member. Alternatively, the protrusion can be formed on the periphery of the lid member.
Within the base member, a functional device such as an electronic component mounted on an alumina substrate is fixed under connection with the lead wires through an electric conductive thread such as a gold or aluminum thread.
As described hereinbefore, the functional device should work sufficiently reliably even under severe conditions. For this reason, the device is hermetically sealed within the package, for instance, by welding the base member to the lid member through resistance welding in vaccum or under dry nitrogen atmosphere. In the welding operation, the applied energy is concentrated on the protrusion so that the top of the protrusion on the base member in contact with the periphery of the lid member is fused to hermetically seal both members.
Until now, the protrusion is formed on either of the members by physical processing such as stamping. For performing the stamping of a metallic sheet to form the protrusion, a fine mold is necessarily employed, and naturally the manufacture of the fine mold is very expensive. Therefore, the heretofore employed process for the preparation of the hermetically sealable package is disadvantageous in the manufacturing cost, and is not appropriate for manufacturing a small number of products. Moreover, the stamping is not appropriate for forming a protrusion having a ridgeline of even height. Accordingly, the sealing is sometimes not attained satisfactorily, and the product yield is not sufficiently high.
In the manufacture of a highly integrated electronic circuit for the use in a high frequency region or other functional devices, the quality check is generally performed in the form of a final product after providing the complete sealing. Heretofore, it has been noted that quite a few of the final products do not show the desired characteristics. The disqualified product can be converted to a qualified product by adjustment of the time constant or exchange of certain functional parts. However, the lid member of the conventional package is not exchangeable after fixation to the base member. Accordingly the above-mentioned adjustment or exchange is not effective in enhancing the production yield.